The present disclosure relates to a sterilization film capable of generating plasma, and in particular, to a wrapping structure, which includes an upper protection layer, an upper electrode, a dielectric barrier film, a lower electrode, and a lower protection layer and is configured to have a similar structure to a retort pouch and generate atmospheric pressure plasma for sterilization.
Japanese Patent Laid-open No. 2008-183025 discloses a plasma sterilization apparatus configured to use an air-permeable wrapping material and to generate a dielectric barrier discharge. Microorganisms in the sterilization apparatus may be killed by oxygen radicals, which are directly generated by the dielectric barrier discharge, or by ozone, OH radical, or hydrogen peroxide, which is generated by the ultraviolet light emitted from the plasma. However, it is difficult to apply the method disclosed in Japanese Patent Laid-open No. 2008-183025 to a liquid target object.
In addition, Korean Patent No. 10-1012442 discloses a plasma sterilization apparatus using atmospheric pressure plasma. However, it is difficult to apply the method disclosed in Korean Patent No. 10-1012442 to a wrapping structure and/or a liquid target object.
Some goods (e.g., food, beverages, and so forth) are individually packaged and delivered to consumers, in order to increase the value of the goods and to protect the goods in the distribution process. Generally, paper, glass, plastic, and so forth may be used as a material for a wrapping container. Especially, in the case of dry foods, plastic packaging containers (e.g., of polyethylene terephthalate (PET)) are used to prevent moisture absorption, discoloration, fat acidification, and flavor deterioration, and an aluminum foil with low moisture and oxygen permeability and good barrier properties is additionally used, in addition to the PET film.
In addition, a gas replacement packaging method has been developed as an improvement measure for a vacuum packaging method. By applying such a gas replacement packaging method, it is possible to reduce the growth rate of microorganisms, delay the deterioration by enzymes, and maintain the color of meat.
However, it is hard to completely prevent growth of microorganisms, even if food is packaged. In addition, in order to sterilize a food product, a sterilization process should be performed before a packaging process, if a high-pressure high-temperature sterilization using a retort pouch is not used. Accordingly, there may be a re-contamination or cross-contamination issue during storage of the food product.
A thermal sterilization process on a retort pouch is considered to be effective and safe, but the thermal sterilization process may lead to physicochemical changes of food such as destruction of nutrients and a change in flavor of the food. In addition, it is hard to apply the thermal sterilization to heat-sensitive food product.
Recently, non-thermal sterilization methods have been developed and commercialized to overcome the disadvantages of the thermal sterilization. For instance, a method using ultraviolet (UV) light, radioactive ray (e.g., gamma ray, electron beam, X-ray), and ultra-high pressure may be used as examples of the non-thermal sterilization method. The ultraviolet light may not be suitable for sterilizing a packaged food product, due to its low permeability. By contrast, the radioactive ray has high permeability, and thus, it can be used to sterilize a fully-packaged food product. However, the radioactive ray sterilization is slowly being commercialized, owing to its enormous initial installation and management costs and low acceptability of consumers. The method using the ultra-high pressure can be used to sterilize a fully-packaged food product, but this method also has a problem of high initial investment cost and physicochemical change of food.
Low-temperature atmospheric-pressure plasma is the solution that is proposed as an alternative to the non-thermal sterilization technology of the packaged food products. A sterilization method using plasma provides great advantages in cost efficiency, mobility and workability, compared to other non-thermal sterilization methods. However, since the low-temperature atmospheric-pressure plasma has low permeability, it is difficult to sterilize a food product in a package using the plasma generated from the outside. If the plasma is generated in the package, a fully packaged food product may be effectively sterilized by the plasma.
A dielectric barrier discharge (DBD) has been proposed as one of conventional methods, and during the DBD, an external electrode is used to apply a voltage using helium or argon gas. In this case, an additional electrode structure is required in addition to the wrapping structure, and moreover, there is a difficulty in sterilizing a curved or thick food product. Reactive nitrogen species (RNS) and reactive oxygen species (ROS) in plasma of nitrogen or oxygen gas provide a better sterilization effect, when compared to the case that atmospheric plasma of helium gas is used. However, under the condition of the atmospheric pressure, a plasma discharge breakdown voltage of nitrogen or oxygen gas is higher than that of helium gas, and thus there is a problem in generating plasma from nitrogen or oxygen gas. In addition, if the wrapping structure does not have a flat shape, it is difficult to generate plasma and to achieve a uniform sterilization effect.
Therefore, it is necessary to develop a plasma generation device using the wrapping container itself. Furthermore, it is necessary to develop a technique for generating atmospheric pressure plasma from nitrogen gas or the air, which is mainly used for food packaging, and for utilizing the plasma for the food sterilization.
Retort pouches are used to wrap a liquid target object, but in certain cases, it is necessary to use a structure capable of selectively performing one of the plasma sterilization and the thermal sterilization on the retort pouches.
Accordingly, inventors of the present patent application have repeatedly studied to develop a technology useful for inhibiting the growth of microorganisms, which may occur during a distribution process, without damage of the wrapping structure and for sterilizing a wrapping structure itself. A wrapping structure proposed by the inventors is configured to allow any of factory operators (e.g., after the wrapping process), retailers, and consumers to perform a sterilization process using atmospheric pressure plasma, before opening the wrapping structure, if a simple power supply is provided.